1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine.
2. Description of the Prior Art
Conventionally, copying machines have been widely used which optically scan a document original, form an electrostatic latent image on a photoreceptor based on the scanned image of the document original, develop the electrostatic latent image into a toner image, and then transfer the toner image onto a sheet of copy paper. These copying machines, if necessary, are provided with an automatic document feeder for feeding document originals one by one, and with a sorter for sorting and outputting copy paper sheets into a plurality of sheet receiving trays when a plurality of copies are made from a single document original.
Such copying machines can form a copy image of a document original not only on a sheet of normal paper, but also on a transparent sheet for an OverHead Projector (hereinafter referred to as an "OHP sheet"). In general, since the image formed on a transparent OHP sheet is illegible, an interleaf sheet is attached onto the back face of the OHP sheet.
When a copy is made on an OHP sheet, an interleaf sheet is attached onto the back face of the OHP sheet by placing the interleaf sheet in the sheet receiving tray before the OHP sheet is outputted into the tray. When copies are made on a plurality of OHP sheets, however, interleaf sheets must be placed in the sheet receiving tray one by one before each of the OHP sheets is outputted into the tray. Performing such an operation manually is extremely troublesome. Therefore, a copying machine having an interleaving copy mode for automatically providing interleaf sheets on the back face of OHP sheets is conventionally used to make copies on the OHP sheets.
In the interleaving copy mode, an interleaf sheet is first discharged into the sheet receiving tray before a copy is made on an OHP sheet, and then the OHP sheet on which a copy image of a document original is formed is outputted onto the interleaf sheet. By repeating this operation, an interleaf sheet can be provided onto the back face of each of the plural OHP sheets.
In many cases, OHP sheets on which images are copied are used as a material for a presentation at a meeting, and in general, document materials which contain the same content as the OHP material are prepared for the participants in the meeting, typically so that the same number of copies are made as the number of participants. That is, normal paper copies are prepared in a number equivalent to the number of the participants.
In a conventional manner, copies are made on OHP sheets in the interleaving copy mode as mentioned above, and then on normal paper sheets by the desired number in a normal copy mode. In such case, if the copying machine has a sorter, a predetermined number of normal paper copies can be sorted and outputted into a plurality of sheet receiving trays.
A copying operation in the interleaving copy mode of the conventional copying machine, in most cases, needs to be followed by a copying operation in the normal paper copy mode. Therefore, the conventional copying machine is inconvenient for making copies both on OHP sheets and on normal paper sheets.